The present invention relates to a method and system for preventing damage to a festoon should a break in a running web occur while the web is being unwound from a rotating roll, being run through the festoon, and then run to a web-using production process.
The inclusion of festoons in systems for controlling the speed and tension of running webs has been recognized as a significant improvement. Such festoons, which are capable of storing variable amounts or quantities of the running web, typically include, in simplified form, a fixed entry idler, a relatively movable dancer and a fixed exit idler. The web runs about the entry idler, the dancer and then the exit idler. A dancer tensioning cylinder assembly is connected with the dancer and is adapted to urge the dancer upwardly, vertically with respect to the fixed idlers and against the force of the web running over and about that dancer.
The dancer tensioning cylinder assembly includes a piston, which is disposed for reciprocal movement within a cylinder, which is connected to the dancer by, for instance, a cable, and to which controlled, pressurized air is applied to one surface or face of the piston so as to force the piston to move in one direction within the cylinder. Upward movement of the dancer may occur in response to movement of the piston in the one direction in the cylinder.
In the past, a break in the running web could and often did cause damage to the festoon. The break would remove the web-generated force that opposed the upwardly directed force imposed on the dancer by the dancer tensioning cylinder assembly. Upon this removal, the dancer would tend to move suddenly, upwardly in the festoon. Such out-of-control, upward movement sometimes caused the dancer to strike the festoon's supporting structure, thus damaging the dancer and/or the festoons supporting structure. Repair of such damage could be costly particularly in terms of the down time of the web-using production process.